In these boom times for 3-D moviemaking, The Secret of Kells is flat and proud of it. Its hand-drawn two-dimensional animation springs to life with color and meticulous technique, filigreed and curlicued like the luminous book at its center.

On the downside, its characters lack depth (figuratively as well as literally), and the plot is standard fare for a family-friendly historical saga: Brave orphan teams up with old coot and young sprite to rescue civilization from encroaching darkness. Adding a dash of the exotic is the story's setting in a ninth-century Irish monastery, where boy monk Brendan (the voice of Evan McGuire) rushes to help master illuminator Aidan (Mick Lally) complete the holy book of Kells before rampaging armies of Norsemen lay waste to all they know.

Helping Brendan: Aisling (Christen Mooney), a mysterious wee girl (or is she?) he meets in the woods. Not helping Brendan: his uncle the Abbot (Brendan Gleeson), an imperious worrier who's preoccupied with fortifying the walls around the abbey. The tension between idealism and pragmatism, between dreamer and builder, mounts as Aidan teaches Brendan the ins and outs of illuminated manuscripts. The faith they have in a single book —“a beacon in the dark days of the northmen” — proves infectious and lifts the movie with flights of thrilling visual invention.

Directed by Tomm Moore and Nora Twomey, The Secret of Kells lavishes attention on its stylized backgrounds and details: Aisling's glorious forest, swirling with butterflies and leaves; mazelike tangles of Celtic imagery; a serpentine monster that kinks like the borders on a page. The artwork is the star of the film, as well it should be; there's no sense making an ugly movie about a medieval tome renowned for its history and beauty.

Nevertheless, the directors and screenwriter (Fabrice Ziolkowski) might have spilled more ink on some of their human characters, who look like minimalist cutouts from Saturday-morning cartoons. Squeezed in among all the Irish brothers at Kells are a few exhausted clichés: an enormous African, a philosophizing German and a jolly Italian who sounds like a refugee from an old Ragu commercial. At least they get faces. The invaders from the north appear as beady-eyed shadows with horns, snarling abstractions that represent the larger forces of evil. (A historical aside that's been itching at me since How to Train Your Dragon: The Vikings did not, in fact, wear horned helmets.)

The Secret of Kellssnagged an Oscar nod this year for best animated feature, an award it had zero hope of winning in a field crammed with unusually fine examples of the genre. But you can see why it was nominated, notwithstanding the slightness of its characters and the slimness of its plot. In its small, stubborn way, the film is a love letter to traditions that have endured since cave dwellers painted the walls at Lascaux. Its own breathtaking artistry is a tribute to the steady hands that drew the Book of Kells — and the steady hands that keep at it today, realizing whole worlds from blank pages.